1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating a liquid crystal display device, and more particularly, to an array substrate for a transflective liquid crystal display device and a method of fabricating the same.
2. Discussion of the Related Art
As the information age advances, display devices for displaying information are actively being developed. More particularly, flat panel display (FPD) devices having a thin profile, light weight and low power consumption are actively being pursued. FPD devices can be classified as either an emissive type or a non-emissive type depending on their light emission capability. In an emissive type FPD device, an image is displayed using light that emanates from the FPD device. In a non-emissive type FPD device, an image is displayed using light from an external source that reflects and/or transmits through the FPD. For example, a plasma display panel (PDP) device is a field emission display (FED) device. In another example, an electroluminescent display (ELD) device is an emissive type FPD device. Unlike a PDP and an ELD, a liquid crystal display (LCD) device is a non-emissive type FPD device that uses a backlight as a light source.
Among the various types of FPD devices, liquid crystal display (LCD) devices are widely used as monitors for notebook computers and desktop computers because of their high resolution, color rendering capability and superiority in displaying moving images. The LCD device displays images by controlling a transmittance of light through the device. More particularly, liquid crystal molecules of a liquid crystal interposed between two substrates facing each other control light transmission in response to an electric field generated between electrodes on one of the substrates.
Because the LCD device does not emit light, the LCD device needs to be used with a separate light source. Thus, a backlight is disposed on the rear surface on a liquid crystal panel of the LCD device, and images are displayed with the light emitted from the backlight and transmitted through the liquid crystal panel. Accordingly, the above-mentioned LCD device is referred to as a transmission type LCD device. The transmission type LCD device can display bright images in a dark environment due to the use of a separate light source, such as a backlight, but may cause a large power consumption because of the use of the backlight.
To solve the problem of large power consumption, a reflection type LCD device has been developed. The reflection type LCD device controls a transmittance of light by reflecting the outside natural light or artificial light through a liquid crystal layer. In a reflection type LCD device, a pixel electrode on a lower substrate is formed of a conductive material having a relatively high reflectance and a common electrode on an upper substrate is formed of a transparent conductive material. Although the reflection type LCD device may have lower power consumption than the transmission type LCD device, it may have low brightness when the outside light is insufficient or weak.
To solve both the problems of large power consumption and low brightness, a transflective LCD device combining the capabilities of a transmission type LCD device and reflection type LCD device has been suggested. The transflective LCD device can select a transmission mode using a backlight while in an indoor environment or a circumstance having no external light source, and a reflection mode using an external light source in an environment where the external light source exists.
FIG. 1 is a cross-sectional view of an array substrate for a transflective LCD device according to the related art. In FIG. 1, a substrate 10 includes a pixel region “P” defined by a crossing of a gate line (not shown) and a data line 30. The pixel region “P” includes a reflective area “RA” and a transmissive area “TA.” The reflective area “RA” includes a transistor area “TrA.”
A thin film transistor (TFT) “Tr,” including a gate electrode 15, a gate insulating layer 20, a semiconductor layer 25, a source electrode 33 and a drain electrode 36, is formed on the substrate 10 in the transistor area “TrA.” The semiconductor layer 25 includes an active layer 25a and an ohmic contact layer 25b. A first passivation layer 39 of an inorganic insulating material is formed on the TFT “Tr” and a second passivation layer 45 of an organic insulating material is formed on the first passivation layer 39. Subsequently, a through hole “TH” is formed in the second passivation layer 45 within the transmissive area “TA.” Further, the second passivation layer 45 includes a drain contact hole 47 exposing the drain electrode 36 and an uneven top surface. A third passivation layer 49 of an inorganic insulating material is formed on the second passivation layer 45 and has the drain contact hole 47 exposing the drain electrode 36. A reflective plate 52 of a reflective metallic material layer is formed on the third passivation layer 49. The reflective plates 52 in the adjacent pixel region “P” are separated from each other. A fourth passivation layer 55 of an inorganic insulating material is formed on the reflective plate 52, and a pixel electrode 60 is formed on the fourth passivation layer 55. The pixel electrode 60 is connected to the drain electrode 36 through the drain contact hole 47. As a result, a gate insulating layer 20 of the thin film transistor (TFT) “Tr,” the first passivation layer 39, the third passivation layer 49, the fourth passivation layer 55 and the pixel electrode 60 are sequentially formed on the substrate 10 in the transmissive area “TA.”
FIGS. 2A to 2F are cross-sectional views showing a fabrication process of an array substrate for a transflective LCD device according to the related art. As shown in FIG. 2A, after a first metal layer (not shown) of a first metallic material is deposited on a substrate 10, a gate electrode 15 and a gate line (not shown) are formed by patterning the first metal layer through a first mask process including a coating step for a photoresist (PR), an exposure step using a mask, a developing step of the PR and an etching step of the first metal layer. The substrate 10 includes a pixel region “P” divided into a transmissive area “TA” and a reflective area “RA.” The reflective area “RA” includes a transistor area “TrA.”
As shown in FIG. 2B, a gate insulating layer 20 is formed on the gate electrode 15 and the gate line. An intrinsic amorphous silicon layer (not shown), a doped amorphous silicon layer (not shown) and a second metal layer (not shown) are sequentially deposited on the gate insulating layer 20. Then, a data line 30, a semiconductor layer 25, including an active layer 25a and an ohmic contact layer 25b, a source electrode 33 and a drain electrode 36, are formed by patterning the second metal layer, the doped amorphous silicon layer and the intrinsic amorphous silicon layer through a second mask process.
As shown in FIG. 2C, a first passivation layer 39 is formed on the source electrode 33, the drain electrode 36 and the data line 30 by depositing an inorganic insulating material. After coating an organic insulating material on the first passivation layer 39, a second passivation layer 45 is formed by patterning the coated organic insulating material through a third mask process. The second passivation layer 45 has an uneven top surface, and includes a drain contact hole 47 and a through hole “TH.” The drain contact hole exposes the first passivation layer 39 on the drain electrode 36 and the through hole “TH” exposes the first passivation layer 39 in the transmissive area “TA.” In addition, a third passivation layer 49 is formed on the second passivation layer 39 by depositing an inorganic insulating material.
As shown in FIG. 2D, after a third metal layer (not shown) having a relatively high reflectance is deposited on the third passivation layer 49, a reflective plate 52 is formed in the reflective area “RA” of the pixel region “P” by patterning the third metal layer through a fourth mask process. Since the third metal layer corresponding to the drain contact hole 47 and the through hole “TH” is removed, the third passivation layer 49 corresponding to the drain contact hole 47 and the through hole “TH” is exposed through the reflective plate 52.
As shown in FIG. 2E, after an inorganic insulating material is deposited on the reflective plate 52, a fourth passivation layer 55 is formed by patterning the deposited inorganic insulating material through a fifth mask process. Since the fourth passivation layer 55, the third passivation layer 49 and the first passivation layer 39 corresponding to the drain contact hole 47 are removed, the drain electrode 36 is exposed through the drain contact hole 47.
As shown in FIG. 2F, after a transparent conductive material is deposited on the fourth passivation layer 55. Then, a pixel electrode 60 is formed in the pixel region “P” by patterning the deposited transparent conductive material through a sixth mask process. Thus, the pixel electrode 60 is connected to the drain electrode 36 through the drain contact hole 47.
As described above, an array substrate for a transflective LCD device according to the related art is fabricated through a six-mask process. Each mask process includes several steps, such as coating PR, exposure of the PR using a mask, a developing the PR, etching using the developed PR and stripping the developed PR. Accordingly, mask processes are expensive in terms of both fabrication time and material cost. In addition, each mask process introduces an additional probability of yield reduction.